Pandas 重置索引深度总结

今天我们来讨论 Pandas 中的 `reset_index()` 方法，包括为什么我们需要在 Pandas 中重置 DataFrame 的索引，以及我们应该如何应用该方法 在本文我们将使用 Kaggle 上的数据集样本 Animal Shelter Analytics 来作为我们的测试数据 ## Pandas 中的 Reset_Index() 是什么？ 如果我们使用 Pandas 的 `read_csv()` 方法读取 csv 文件而不指定任何索引，则生成的 DataFrame 将具有默认的基于整数的索引，第一行从 0 开始，随后每行增加 1： ```Python import pandas as pd import numpy as np df = pd.read_csv('Austin_Animal_Center_Intakes.csv').head() df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 在某些情况下，我们可能希望拥有更有意义的行标签，因此我们将选择 DataFrame 的其中一列作为 DataFrame 索引。我们可以使用 `read_csv()` 方法的 index_col 参数直接执行此操作： ```Python df = pd.read_csv('Austin_Animal_Center_Intakes.csv', index_col='Animal ID').head() df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 或者我们还可以使用 set_index() 方法将 DataFrame 的任何列设置为 DataFrame 索引： ```Python df = pd.read_csv('Austin_Animal_Center_Intakes.csv').head() df.set_index('Animal ID', inplace=True) df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 如果在某个时候我们需要恢复默认的数字索引呢，这时就可以使用 reset_index()函数了 ```Python df.reset_index() ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 此方法的默认行为包括用默认的基于整数的索引替换现有的 DataFrame 索引，并将旧索引转换为与旧索引同名的新列（或名称索引）。此外，默认情况下，reset_index() 方法会从 MultiIndex 中删除所有级别并且不会影响原始 DataFrame 数据，而是创建一个新的 ## 何时使用 Reset_Index() 方法 reset_index() 方法将 DataFrame 索引重置为默认数字索引，在以下情况下特别有用： - 执行数据整理时——尤其是过滤数据或删除缺失值等预处理操作，会导致较小的 DataFrame 具有不再连续的数字索引 - 当索引应该被视为一个常见的 DataFrame 列时 - 当索引标签没有提供有关数据的任何有价值的信息时 ## 如何调整 Reset_Index() 方法 前面的讨论中，我们看到了当我们不向它传递任何参数时，reset_index() 方法是如何工作的，当然如果有需要，我们可以通过调整方法的各种参数来更改此默认行为。 让我们看看最有用的三种参数：level、drop 和 inplace ### level 此参数采用整数、字符串、元组或列表作为可能的数据类型，并且仅适用于具有 MultiIndex 的 DataFrame，如下所示： ```Python df_multiindex = pd.read_csv('Austin_Animal_Center_Intakes.csv', index_col=['Animal ID', 'Name']).head() df_multiindex ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 事实上，如果现在我们检查上面 DataFrame 的索引，我们会发现它不是一个常见的 DataFrame 索引，而是一个 MultiIndex 对象： ```Python df_multiindex.index ``` Output: ```Text MultiIndex([('A786884', '*Brock'), ('A706918', 'Belle'), ('A724273', 'Runster'), ('A665644', nan), ('A682524', 'Rio')], names=['Animal ID', 'Name']) ``` 默认情况下，reset_index() 方法参数 level (level=None) 会移除 MultiIndex 的所有级别： ```Python df_multiindex.reset_index() ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 我们看到 DataFrame 的两个索引都被转换为通用 DataFrame 列，而索引被重置为默认的基于整数的索引 相反，如果我们显式传递 level 的值，则此参数会从 DataFrame 索引中删除选定的级别，并将它们作为常见的 DataFrame 列返回（除非我们选择使用 drop 参数从 DataFrame 中完全删除此信息）。比较以下操作： ```Python df_multiindex.reset_index(level='Animal ID') ``` Output: ```Text Name Animal ID DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color *Brock A786884 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor Belle A706918 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver Runster A724273 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White NaN A665644 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico Rio A682524 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 最开始 Animal ID 是 DataFrame 的索引之一，当我们设置 level 参数后，将其从索引中删除并作为称为 Animal ID 的公共列插入到 DataFrame 中 ```Python df_multiindex.reset_index(level='Name') ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 在这里，Name 最初是 DataFrame 的索引之一，设置完level参数后，就变成了一个常用的列，叫做Name ### drop 此参数决定在索引重置后是否将旧索引保留为通用 DataFrame 列，或者将其从 DataFrame 中完全删除。默认情况下 (drop=False) 是进行保留的，正如我们在前面的所有示例中看到的那样。否则，如果我们不想将旧索引保留为列，我们可以在索引重置后将其从 DataFrame 中完全删除（drop=True）： ```Python df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 增加 drop 参数 ```Python df.reset_index(drop=True) ``` Output: ```Text Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 在上面的 DataFrame 中，旧索引中包含的信息已完全从 DataFrame 中删除了 drop 参数也适用于具有 MultiIndex 的 DataFrame，就像我们之前创建的那样： ```Python df_multiindex ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 增加 drop 参数 ```Python df_multiindex.reset_index(drop=True) ``` Output: ```Text DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 两个旧索引都已从 Dataframe 中完全删除，并且索引已重置为默认值 当然，我们可以结合 drop 和 level 参数，指定要从 DataFrame 中完全删除哪些旧索引： ```Python df_multiindex.reset_index(level='Animal ID', drop=True) ``` Output: ```Text DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color Name *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 旧索引 Animal ID 已从索引和 DataFrame 本身中删除，另一个索引 Name 被保留为 DataFrame 的当前索引 ### inplace 该参数决定是直接修改原来的 DataFrame 还是新建一个 DataFrame 对象。默认情况下，它会使用新索引 (inplace=False) 创建一个新的 DataFrame，并保持原始 DataFrame 不变。让我们使用默认参数再次运行 reset_index() 方法，然后将结果与原始 DataFrame 进行比较： ```Python df.reset_index() ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` ```Python df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 即使我们将索引重置为运行第一段代码的默认数字，原始 DataFrame 仍然保持不变。 如果我们需要将原始 DataFrame 重新分配给对其应用 reset_index() 方法的结果，我们可以直接重新分配它（df = df.reset_index()）或将参数 inplace=True 传递给该方法： ```Python df.reset_index(inplace=True) df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 我们看到现在更改已直接应用于原始 DataFrame 之上了 ## 应用实例：删除缺失值后重置索引 让我们将到目前为止讨论的所有内容付诸实践，看看当我们从 DataFrame 中删除缺失值时，重置 DataFrame 索引是如何有用的 首先，让我们恢复我们最开始时创建的第一个 DataFrame，它具有默认数字索引： ```Python df = pd.read_csv('Austin_Animal_Center_Intakes.csv').head() df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A665644 NaN 10/21/2013 07:59:00 AM 10/21/2013 07:59:00 AM Austin (TX) Stray Sick Cat Intact Female 4 weeks Domestic Shorthair Mix Calico 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 我们看到 DataFrame 中有一个缺失值，让我们使用 dropna() 方法删除具有缺失值的整行 ```Python df.dropna(inplace=True) df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 该行已从 DataFrame 中删除，但是索引不再是连续的：0、1、2、4。让我们重新设置它： ```Python df.reset_index() ``` Output: ```Text index Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 4 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 现在索引是连续的了，但是由于我们没有显式传递 drop 参数，旧索引被转换为列，具有默认名称 index，下面让我们从 DataFrame 中完全删除旧索引： ```Python df.reset_index(drop=True) ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` 现在我们彻底摆脱了无意义的旧索引，当前索引是连续的。最后一步是使用 inplace 参数将这些修改保存到我们的原始 DataFrame 中： ```Python df.reset_index(drop=True, inplace=True) df ``` Output: ```Text Animal ID Name DateTime MonthYear Found Location Intake Type Intake Condition Animal Type Sex upon Intake Age upon Intake Breed Color 0 A786884 *Brock 01/03/2019 04:19:00 PM 01/03/2019 04:19:00 PM 2501 Magin Meadow Dr in Austin (TX) Stray Normal Dog Neutered Male 2 years Beagle Mix Tricolor 1 A706918 Belle 07/05/2015 12:59:00 PM 07/05/2015 12:59:00 PM 9409 Bluegrass Dr in Austin (TX) Stray Normal Dog Spayed Female 8 years English Springer Spaniel White/Liver 2 A724273 Runster 04/14/2016 06:43:00 PM 04/14/2016 06:43:00 PM 2818 Palomino Trail in Austin (TX) Stray Normal Dog Intact Male 11 months Basenji Mix Sable/White 3 A682524 Rio 06/29/2014 10:38:00 AM 06/29/2014 10:38:00 AM 800 Grove Blvd in Austin (TX) Stray Normal Dog Neutered Male 4 years Doberman Pinsch/Australian Cattle Dog Tan/Gray ``` ## 总结 今天我们从多个方面讨论了 reset_index() 方法 - reset_index() 方法的默认行为 - 如何恢复 DataFrame 的默认数字索引 - 何时使用 reset_index() 方法 - 该方法最重要的几个参数 - 如何使用 MultiIndex - 如何从 DataFrame 中完全删除旧索引 - 如何将修改直接保存到原始 DataFrame 中 最好我们又完整的完成了一个在删除缺失值后重置 DataFrame 索引的实战案例 好了，这就是今天分享的全部内容，喜欢就点个赞吧 本文由[mdnice](https://mdnice.com/?platform=6)多平台发布
©著作权归作者所有,转载或内容合作请联系作者
  • 人面猴
    序言：七十年代末，一起剥皮案震惊了整个滨河市，随后出现的几起案子，更是在滨河造成了极大的恐慌，老刑警刘岩，带你破解...
    沈念sama阅读 202,529评论 5赞 475
  • 死咒
    序言：滨河连续发生了三起死亡事件，死亡现场离奇诡异，居然都是意外死亡，警方通过查阅死者的电脑和手机，发现死者居然都...
    沈念sama阅读 85,015评论 2赞 379
  • 救了他两次的神仙让他今天三更去死
    文/潘晓璐 我一进店门，熙熙楼的掌柜王于贵愁眉苦脸地迎上来，“玉大人，你说我怎么就摊上这事。” “怎么了？”我有些...
    开封第一讲书人阅读 149,409评论 0赞 335
  • 道士缉凶录：失踪的卖姜人
    文/不坏的土叔 我叫张陵，是天一观的道长。 经常有香客问我，道长，这世上最难降的妖魔是什么？ 我笑而不...
    开封第一讲书人阅读 54,385评论 1赞 273
  • 港岛之恋（遗憾婚礼）
    正文 为了忘掉前任，我火速办了婚礼，结果婚礼上，老公的妹妹穿的比我还像新娘。我一直安慰自己，他们只是感情好，可当我...
    茶点故事阅读 63,387评论 5赞 364
  • 恶毒庶女顶嫁案：这布局不是一般人想出来的
    文/花漫 我一把揭开白布。 她就那样静静地躺着，像睡着了一般。 火红的嫁衣衬着肌肤如雪。 梳的纹丝不乱的头发上，一...
    开封第一讲书人阅读 48,466评论 1赞 281
  • 城市分裂传说
    那天，我揣着相机与录音，去河边找鬼。 笑死，一个胖子当着我的面吹牛，可吹牛的内容都是我干的。 我是一名探鬼主播，决...
    沈念sama阅读 37,880评论 3赞 395
  • 双鸳鸯连环套：你想象不到人心有多黑
    文/苍兰香墨 我猛地睁开眼，长吁一口气：“原来是场噩梦啊……” “哼！你这毒妇竟也来了？” 一声冷哼从身侧响起，我...
    开封第一讲书人阅读 36,528评论 0赞 256
  • 万荣杀人案实录
    序言：老挝万荣一对情侣失踪，失踪者是张志新（化名）和其女友刘颖，没想到半个月后，有当地人在树林里发现了一具尸体，经...
    沈念sama阅读 40,727评论 1赞 295
  • 护林员之死
    正文 独居荒郊野岭守林人离奇死亡，尸身上长有42处带血的脓包…… 初始之章·张勋 以下内容为张勋视角 年9月15日...
    茶点故事阅读 35,528评论 2赞 319
  • 白月光启示录
    正文 我和宋清朗相恋三年，在试婚纱的时候发现自己被绿了。 大学时的朋友给我发了我未婚夫和他白月光在一起吃饭的照片。...
    茶点故事阅读 37,602评论 1赞 329
  • 活死人
    序言：一个原本活蹦乱跳的男人离奇死亡，死状恐怖，灵堂内的尸体忽然破棺而出，到底是诈尸还是另有隐情，我是刑警宁泽，带...
    沈念sama阅读 33,302评论 4赞 318
  • 日本核电站爆炸内幕
    正文 年R本政府宣布，位于F岛的核电站，受9级特大地震影响，放射性物质发生泄漏。R本人自食恶果不足惜，却给世界环境...
    茶点故事阅读 38,873评论 3赞 306
  • 男人毒药：我在死后第九天来索命
    文/蒙蒙 一、第九天 我趴在偏房一处隐蔽的房顶上张望。 院中可真热闹，春花似锦、人声如沸。这庄子的主人今日做“春日...
    开封第一讲书人阅读 29,890评论 0赞 19
  • 一桩弑父案，背后竟有这般阴谋
    文/苍兰香墨 我抬头看了看天上的太阳。三九已至，却和暖如春，着一层夹袄步出监牢的瞬间，已是汗流浃背。 一阵脚步声响...
    开封第一讲书人阅读 31,132评论 1赞 259
  • 情欲美人皮
    我被黑心中介骗来泰国打工， 没想到刚下飞机就差点儿被人妖公主榨干…… 1. 我叫王不留，地道东北人。 一个月前我还...
    沈念sama阅读 42,777评论 2赞 349
  • 代替公主和亲
    正文 我出身青楼，却偏偏与公主长得像，于是被迫代替她去往敌国和亲。 传闻我的和亲对象是个残疾皇子，可洞房花烛夜当晚...
    茶点故事阅读 42,310评论 2赞 342

推荐阅读更多精彩内容